TROUBLESHOOTING AND REPAIR
RF LEVEL/AM
Output PCA Q9 Bias Adjustment, R1 6D-22.
The following procedure covers the bias adjustment of Q9 on the Output PCA.
TEST EQUIPMENT:
• Spectrum analyzer
REMARKS:
This adjustment is normally made only when Q9 or associated circuitry is replaced.
PROCEDURE:
Rl adjusts the collector current of Q9 to minimize harmonic distortion.
1. Remove the bottom instrument cover, bottom module plate cover, and the pulse
cover.
2. Connect UUT RF Output to the spectrum analyzer. Set the spectrum analyzer
sweep to cover the frequency range of 1 to 1300 MHz and set the analyzer reference
level to +13 dBm.
3. Set UUT to SPCL 01 and amplitude to +13 dBm.
4. Edit the frequency to display signal and harmonics on the spectrum analyzer.
Adjust R1 to minimize the worst harmonic seen. This is typically the second
harmonic with the UUT frequency at about 300 MHz. The harmonic must be less
than 30 dBc for proper operation.
5. Reinstall the pulse cover, the module plate cover, and the instrument cover.
Output PCA Gain Flatness Adjustment, C201 6D-23.
This procedure describes the adjustment of C201 for the purpose of optimizing gain
flatness. This adjustment should not be required unless CR20 (detector diode) or parts
in the RF path following C180 are replaced. This adjustment should be followed by
output compensation. See Appendix H.
TEST EQUIPMENT:
• Power meter
• Tuning tool, .025 in. square, Johanson #4192
PROCEDURE:
1. Zero the power meter
2. Program the UUT to SPCL 01, 350 MHz, and +7 dBm. Connect the power meter
to the UUT RF output.
3. Set the power meter to dB REF.
4. Edit the UUT frequency from 15 to 1056 MHz and note the variation in level.
Adjust C201 to minimize the level variation. C201 will have the greatest effect at
high frequencies. Level should be flat with a maximum allowed variation of 3dB.
6D-19
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